To improve automotive engine fuel economy, a current objective in the design of valve trains is weight and friction reduction. This has been accomplished in the past, for example, by the use of stamped steel rocker arms instead of heavier forged or cast arms, and the use of roller bearings between the engine cam and rocker arm surface for reducing friction. A switch to finger follower lever type rocker arms also has reduced weight and complexity and friction; but, in general, these latter type constructions generally employ only a cylindrical surface or an axle type roller rotatable on needle bearings or bronze bushings.
For example, U.S. Pat. No. 2,081,390 to Trapp, U.S. Pat. No. 3,977,370 to Humphreys, U.S. Pat. No. 3,137,283 to Sampietro, and U.S. Pat. No. 3,108,580 to Crane, Jr., all show the use of rollers in cam followers for reducing friction and weight between the parts. However, it will be noted then in each of the instances, the rollers all have axles, generally with roller bearings or other suitable low friction parts. This not only complicates the construction but increases the weight and cost of manufacture. Furthermore, in most instances, the rollers are located above the cam and are not self-lubricating, i.e., the recesses in which they are located will not retain oil or other lubricant when the engine is shut down.
U.S. Pat. No. 1,363,398 to Davids, U.S. Pat. No. 1,210,871 to Suffa, and U.S. Pat. No. 1,409,878 to Mainland, are other examples of push rod type valve lifters in which a ball or roller is received in a cage but is movable only in a vertical direction and is retained in a housing that is difficult to machine and generally without consideration of weight reduction.
U.S. Pat. No. 2,151,832 to Bugatti shows a finger follower type rocker arm assembly in which a ball is used between the cam and tappet. However, in this case, a number of balls/rollers are required for rolling against their bearing surfaces, and a retainer is additionally required to maintain the intermediate roller in place. The size and weight of this construction would be excessive, and the roller does not slide in the lever bearing surface but rolls against the other rollers. Also, the cam being located below the lever prevents retention of lubricant for the rolling bearing surfaces upon engine shutdown.
U.S. Pat. No. 4,204,814 to Matzen also shows a construction in which the roller performs a dual function of being an axle and a camshaft follower. It is contained within a two-piece roller shaft 18 which, from a construction standpoint, provides alignment problems for the split bearing surface. Furthermore, while a gap 14 is provided for the introduction of lubricant or oil to the roller, upon engine shutdown, the lubricant will drain out and provide a dry start for the next cycle.
U.S. Pat. No. 4,406,257 to Keske et al. shows a roller follower in which a roller 30 has in effect a pair of laterally extending axles 34, 36 supported upon bearing surfaces 26, 28, each part of a two-piece support, the central portion of the roller being interdigited with the support. The cam follower surface, therefore, is separate from the rolling surface. The construction as disclosed is difficult to machine and assemble the bearing surfaces 26, 28 with precision in order to avoid edge riding of the bearing. Neither friction nor weight appears to be minimized with such construction.